To overcome the limitations of current urine-based diagnostic assays of urogenital tuberculosis, we used isothermal microcalorimetry to detect the metabolic activity of Mycobacterium tuberculosis and other commonly neglected pathogenic mycobacteria in urine and accurately determine their growth parameters.

A microcalorimeter equipped with 48 channels was used. Detection was accomplished, and growth was monitored for 4 different Mycobacterium species in sterilized and modified urine at 37°C by measuring metabolic heat flow (μW = μJ/s) as a function of time. These strains were M. smegmatis, M. phlei, M. kansasii, and M. tuberculosis. The data were integrated to perform curve fitting and extract the growth parameter from the raw data.

In sterilized urine, M. smegmatis showed the fastest growth rate (0.089 ± 0.017 [h⁻¹]), followed by M. phlei (0.072 ± 0.016 [h⁻¹]) and M. kansasii (0.007 ± 0.001 [h⁻¹]). No growth of M. tuberculosis was detected in sterilized urine. However, in serum-supplemented urine, growth of M. tuberculosis was observed within 3 weeks at a growth rate of 0.008 ± 0.001 [h⁻¹]. Biofilm formation was enhanced in the serum supplemented urine.

Isothermal microcalorimetry allows rapid and accurate detection of mycobacterial growth in urine. Given the absence of data on the mycobacterial growth in urine, isothermal microcalorimetry could be used to unravel key aspects of Mycobacterium physiology in the urinary tract and potentially contribute to improvement in the diagnosis and treatment of urogenital tuberculosis.